The aggressive scaling of complementary metal-oxide-semiconductor (CMOS) technologies has led to fabrication of semiconductor devices that integrate high-speed digital circuits with high performance analog circuits and radio frequency circuits. In these semiconductor devices, substrate coupling of noise can adversely performance.
CMOS devices are formed from doped semiconductors. During doping, impurity atoms are introduced to an intrinsic semiconductor using a process such as diffusion or ion implantation Impurity atoms are atoms of a different element than the atoms of the intrinsic semiconductor Impurity atoms act as either donors or acceptors to the intrinsic semiconductor, changing the electron and hole concentrations of the semiconductor. A doped semiconductor acts more like a conductor than a semiconductor.
Impurity atoms are classified as either donor or acceptor atoms based on the effect they have on the intrinsic semiconductor. Donor impurity atoms have more valence electrons than the atoms they replace in the intrinsic semiconductor lattice. Donor impurities “donate” their extra valence electrons to a semiconductor's conduction band, providing excess electrons to the intrinsic semiconductor. Excess electrons increase the electron carrier concentration of the semiconductor, making it N type. Acceptor impurity atoms have fewer valence electrons than the atoms they replace in the intrinsic semiconductor. They “accept” electrons from the semiconductor's valence band. This provides excess holes to the intrinsic semiconductor. Excess holes increase the hole carrier concentration of the semiconductor, creating a P type semiconductor. Doping can range from light to heavy. When one dopant atom is added per 100 million atoms, the doping is said to be light. When many more dopant atoms are added, on the order of one per 10,000 atoms, the doping is referred to as heavy. Heavy doping is often indicated by N+ for N type or P+ for P type.
CMOS is a technology for constructing semiconductor devices. The term “complementary” refers to a design style in which complementary pairs of P type and N type metal oxide semiconductor field effect transistors (MOSFETs) are created for use in circuits. As is known in the art, N type MOSFETs (hereinafter “NMOS devices”) are typically fabricated in a P substrate. Also, it is common to fabricate P type MOSFETs (hereinafter “PMOS devices”) in N wells situated within the same P substrate. The present disclosure will be described with reference to CMOS technology, it being understood the present disclosure should not be limited thereto.